1. Field of the Invention
The present invention relates generally to improved duct burner apparatus and method, and more particularly, to improved burner apparatus and method for burning a gaseous fuel in the presence of a flowing oxygen-containing gas stream.
2. Description of the Prior Art
A variety of apparatus for burning a gaseous fuel in the presence of a flowing gas stream, i.e., duct burner apparatus, have been developed and utilized heretofore. Such apparatus are most often utilized in applications where it is advantageous or necessary to add heat to a previously heated oxygen-containing gas stream. For example, the temperature of the hot oxygen-containing gases discharged from a gas turbine is in the range of from about 800.degree. F. to 1200.degree. F. In order to prevent the waste of the heat contained in such turbine exhaust gases, they are often utilized for further process heating. Adding heat to the exhaust gases by means of duct burner apparatus prior to utilizing the gases in process heating applications offers improved heat recovery efficiency with minimum mechanical components. U.S. Pat. No. 3,366,373 issued Jan. 30, 1968 discloses burner apparatus for adding heat to gas turbine exhaust gases flowing through a duct whereby the heated gases can be utilized for producing steam in waste heat boiler or the like.
Various duct burners and duct burner assemblies have been developed which include a fuel gas supply conduit or system of conduits positioned in the path of a flowing oxygen-containing gas stream to be heated. Fuel discharge ports for introducing fuel gas into the oxygen-containing gas stream are disposed in the conduit or conduits and baffle means are attached to the conduit or conduits for providing a relatively quiescent fuel gas ignition zone whereby combustion takes place within and downstream stream of the zone. Examples of such burners and burner assemblies or systems are shown in U.S. Pat. Nos. 3,574,507 issued Apr. 13, 1971; 3,732,059 issued May 8, 1973; 3,843,309 issued Oct. 22. 1974; and 4,523,905 issued June 18, 1985.
While the duct burners and duct burner assemblies utilized heretofore have achieved varying degrees of success, they all suffer from certain disadvantages which affect their operation and service lives. The most severe such disadvantage is the warpage and resultant deterioration of the fuel gas supply conduits and baffles attached thereto as a result of uneven heating from radiation and/or flame impingement. That is, in prior duct burner apparatus, the arrangement of fuel gas supply conduit and baffles for defining a flame holding ignition zone has been such that the combustion of the fuel gas takes place in close proximity to one side of the fuel gas conduit. The resulting radiation and/or flame impingement on that side of the conduit causes the conduit to be unevenly heated which sets up stresses therein and results in warpage and rapid deterioration.
Another disadvatange in prior duct burner apparatus is that the fuel gas is often discharged through fixed fuel gas discharge ports disposed in the fuel gas supply conduit. As a result, the ports cannot be changed or cleaned without involving a major equipment removal and replacement operation. Other disadvantages include long flame length, poor turn down, i.e., inefficient combustion at low fuel gas rates, poor heat distribution into the gas stream being heated and high emissions of atmosphere polluting compounds.
By the present invention, an improved duct burner apparatus and assembly for burning a gaseous fuel in the presence of a flowing oxygen-containing gas stream are provided with obviate the disadvantages mentioned above.